1. Field of the Invention
The present invention relates to a method and apparatus for application of a liquid or pasty medium on a traveling material web, notably of paper or cardboard.
2. Description of the Related Art
An apparatus for application of a liquid or pasty medium on a traveling material web working in compliance with a conventional method is known, e.g., from U.S. Pat. No. 4,848,268. In this apparatus, two applicator rolls rotating in opposite directions form between themselves a press nip through which the traveling material web passes. Assigned to each applicator roll is an applicator mechanism which applies the liquid or pasty medium via an applicator pressure chamber and a doctor on the surface of the applicator roll. The medium applied on the applicator roll surface is then carried, due to the rotation of the applicator roll, in the press nip between the two applicator rolls. There, the medium is transferred from the roll surface to the relevant side of the material web and pressed at the same time into the material web. This method of application is called indirect application. With both applicator mechanisms in operation, the traveling material web is in this way coated on both sides with the liquid or pasty medium. In another embodiment of the this prior apparatus, also described in U.S. Pat. No. 4,848,268, the pressure chamber applicators are replaced by such forming a sump with an exposed liquid surface and applying the medium from the sump via a doctor on the surface of the applicator roll.
While good results as such are achieved with this indirect application method and pertaining applicators, contaminations are able to separate out of the paper or cardboard of the material web as the medium is pressed in the material web in the press nip, however, and accumulate on the surface of the applicator rolls. This can happen especially with material webs consisting predominantly of recycled paper. Such contaminations accumulated on the roll surface then soil the applicators and can ultimately striate the application film on the applicator roll surface, which striae will then be visible also on the product, i.e., on the coated material web.
What is needed in the art is a method and apparatus enabling the high-quality application of a liquid or pasty medium on a traveling material web, without contaminations contained in or on the material web being able to degrade the quality of application.
In the method according to the invention, a liquid or pasty medium is applied on at least one side of the traveling paper web in a direct application.
The liquid or pasty medium applied on at least one side of the material web is then pressed in the traveling material web in a separate step. Hence, the direct application of the medium on the material web and pressing the medium in the material web are separate process steps. Since the pressing step follows the application step in the direction of travel of the material web, any dirt particles or contaminants that may separate from the material web in pressing can no longer proceed to the preceding region of application in which the medium is applied on the material web. The separated particles or contaminants can be removed without difficulty in the region of the separate pressing step, and are thus unable after separation to proceed onto the material web and cause impairments of the quality of application. Besides, separation of dirt particles from the material web in the pressing process is a considerably rarer occurrence in the method according to the invention, since the material web was previously coated already with the liquid or pasty medium. Smaller dirt particles are in this way harmlessly incorporated in the applied medium, thereby reducing dirt particle separations while the medium is pressed in the traveling paper web.
In one embodiment of the method for double-sided application of a liquid or pasty medium on a traveling paper web, the liquid or pasty medium intended for each side of the material web is at the same time applied directly on the traveling material web, and the applied medium is subsequently pressed in the traveling material web on both sides simultaneously. This results in a compact two-step process for double-sided application of a liquid or pasty medium on a traveling material web.
Another embodiment of the inventional method for double-sided application of a liquid or pasty medium on a traveling material web includes the following steps:
To begin with, the liquid or pasty medium is applied directly on one side of the traveling material web. In a following step, the medium applied previously on one side of the material web is separately pressed in the traveling material web. This is followed by a third process step, applying the liquid or pasty medium directly on the other side of the traveling material web. In a following fourth step, the medium applied previously on the other side of the material web is pressed separately in the traveling material web. Thus, the double-sided application of a liquid or pasty medium on a traveling material web occurs in this embodiment in four successive steps performed in the direction of material web passage.
The direct application of a desired final amount of application of liquid or pasty medium on any side of the traveling material web can in the previously described variants of the inventional method suitably be carried out in a single application step. In other words, the medium is preferably applied directly on the material web in a single operation, in a way such that the applied amount matches the desired final amount of application. The result is a compact process.
In a further embodiment of the invention, every step of the direct application of the liquid or pasty medium on any side of the traveling material web is divided in the following partial steps:
A first partial step serves to predose a surplus amount of liquid or pasty medium on the relevant side of the material web. A following separate second step consists in the final dosing of the predosed medium quantity applied previously on the respective side of the material web, to the desired final amount of application.
Instead of a direct application finished-dosed in a single step, the direct application of the medium can thus be subdivided according to the embodiment explained above, as desired in two steps, namely a predosing step and a final dosing step. If desired, both embodiments may also be combined, e.g., to the effect that the direct application of the medium on one side of the traveling material web takes place in a single finish-dosing step, while the direct application of the medium on the other side of the material web occurs in a predosing and a final dosing step. This may be suitable, e.g., when it is desired to apply on the two sides of the material web mediums of different consistency, of which one medium allows easy application in a single finish-dosing step, whereas the other medium can be applied better in separate predosing and finish-dosing steps.
A first inventional apparatus for application of a liquid or pasty medium on a traveling material web, notably of paper or cardboard, includes:
an applicator for direct application of a liquid or pasty medium on one side of the traveling material web,
a rotating mating surface carrying the traveling material web along a contact section, and
a press roll rotating relative to the mating surface in opposite direction and serving to press liquid or pasty medium applied on one side of the material web into the traveling material web.
The contact section of the material web on the mating surface, based on the travel direction of the material web, has coordinated with it first the applicator and, spaced from it, then the press roll, with press roll and mating surface forming a nip through which the material web is passed while carried on the contact section of the mating surface.
In other words, the traveling material web is supported along a contact section on the surface of the mating face, and along this contact section on the surface an applicator for direct application of the medium is coordinated first with the material web and thereafter a press roll for pressing the medium into the web. Applying the medium and pressing it in are thus spatially separated from one another, and dirt particles which in pressing may separate from the traveling material web proceed only on the surface of the press roll, where they can be removed, for example by means of a suitable cleaning apparatus. But separated dirt particles cannot proceed in the applicator and thereby impair the quality of the application.
An embodiment of the inventional first apparatus for double-sided application of a liquid or pasty medium on a traveling material web includes:
a second mating face rotating in a direction opposite to that of the first mating face and, based on the pass-through direction of the material web, following said mating face at a distance, with the traveling material web being carried on the surface of the second mating face along a contact section in a manner such that the material web side provided already with the medium bears on the surface,
a second applicator for direct application of a liquid or pasty medium on one side of a traveling material web, and
a second press roll rotating in a direction opposite to that of the second mating face and serving to press liquid or pasty medium applied on one side of the traveling material web into the traveling material web.
Coordinated with the contact section of the material web on the surface of the second mating face, relative to the pass-through direction of the material, is first the second applicator and thereafter, at a distance, the second press roll, with the second press roll forming with the second mating face a press nip through which the material web is carried while bearing on the contact section of the second mating face.
In other words, the first inventional apparatus for coating one side of the traveling material web is in this embodiment of the invention followed by an identical apparatus for coating the other side of the traveling material web. This results in two mating faces rotating in mutually opposite directions and carrying the traveling material web first on its one side and then on its other. Coordinated with each mating face, in pass-through direction of the material web, is first an applicator and then a press roll.
A second inventional apparatus for application of a liquid or pasty medium on a traveling material web, notably of paper or cardboard, includes:
an applicator for direct application of a liquid or pasty medium on one side of the traveling material web,
a rotating mating face on the surface of which the traveling material web is carried along a contact section,
a press roll rotating in a direction opposite to that of the mating face and serving to press liquid or pasty medium applied on one side of the material web into the traveling web, and
a press roll mating roll rotating in a direction opposite to that of the press roll.
The applicator is coordinated with the contact section of the material web on the surface of the mating face, while the press roll, based on the pass-through direction of the material web, is coordinated with the side of the material web provided previously with medium by the applicator, at a distance after the mating face, and forms with the press roll mating roll a press nip through which the traveling material web is passed.
In other words, the applicator is in this second inventional apparatus coordinated with the mating face, and the press roll has assigned to it a mating roll of its own, whereas in the previously illustrated first apparatus according to the invention the applicator and the press roll were coordinated with a common mating face.
A favorable embodiment of a second inventional apparatus for double-sided application of a liquid or pasty medium on a traveling material web includes:
a second mating face rotating relative to the first press roll in the same direction and following said mating face at a distance, based on the pass-through direction of the material web, with the traveling material web being carried on the surface of the second mating face along a contact section in a manner such that the side of the material web provided already with the medium bears on the roll surface,
a second applicator for direct application of a liquid or pasty medium on one side of a traveling material web,
a second press roll rotating relative to the second mating face in opposite direction and serving to press liquid or pasty medium applied on one side of the material web in the traveling material web, and
a second press roll mating roll rotating in a direction opposite to that of the second press roll.
The second applicator is coordinated with the contact section of the material web on the surface of the second mating face, and the second press roll is coordinated, spaced behind the second mating face, based on the pass-through direction of the material web, with the side of the material web provided previously with the medium by the second applicator, and it forms with the second press roll mating roll a press nip through which the traveling material web is passed.
In other words, the second inventional apparatus for coating one side of the traveling material web is in this embodiment followed by an identical apparatus for coating the other side of the traveling material web. Each applicator has assigned to it a mating face of its own, and each press roll a mating roll of its own.
In the inventional apparatus illustrated above, the rotating mating faces are fashioned preferably as rotating mating rolls. But the rotating mating faces may as well be fashioned as revolving endless belts. Such revolving endless belts are then carried across pertaining drive rolls, reversing rolls, idler rolls and/or sliding shoes or press shoes.
A third inventional apparatus for double-sided application of a liquid or pasty medium on a traveling material web, notably of paper or cardboard, includes:
two applicators (which may be of the same type) each of which applies a liquid or pasty medium directly on one of the two sides of the traveling material web, and
two press rolls of same type that rotate in opposite directions and each of which presses the liquid or pasty medium applied on the relevant one of the two sides of the material web into the traveling material web.
The two applicators oppose one another and are coordinated each with one side of the traveling material web in a manner such that the material web passes through between the two applicators. Furthermore, based on the pass-through direction of the material web, the two press rolls are arranged at a distance after the two applicators, in a fashion such that the two press rolls form between them a press nip through which the traveling material web passes, with the running directions of the two press rolls corresponding in the press nip with the pass-through direction of the material web.
Hence, the third inventional apparatus applies first a coat of liquid or pasty medium directly on both sides of the material web, in that the web is passed through between the two applicators, while the previously applied medium is then on both sides pressed in the material web by passing the web between two press rolls that rotate in a direction corresponding to that of the material web passage.
In the third inventional apparatus illustrated above, the pass-through direction of the material web, based on a horizontal plane, is in a favorable embodiment from bottom to top. Preferably, the material web passes through between the two applicators and the two press rolls in a common plane.
In one embodiment of the inventional apparatus illustrated above, the applicators are fashioned as doctor/pressure chamber applicators. The doctors are preferably designed as profiled doctor bars, smooth doctor bars or doctor blades. Using profiled doctor bars is favorable insofar as the medium to be applied is dosed volumetrically, that is, the amount of medium applied is virtually independent of the machine speed. Thus, the desired amount of liquid or pasty medium can be applied very reliably.
In a further embodiment of the inventional apparatus, the applicators may be designed as such featuring open-jet nozzles.
A favorable embodiment of the third inventional apparatus illustrated above is constituted by fashioning the applicators as doctor applicators forming a sump of the medium being applied with an exposed liquid surface. The pertaining pass-through direction of the material web through the two sump applicators is then from top to bottom, based on a horizontal plane. The doctors of the sump applicators are preferably designed as profiled doctor bars, smooth doctor bars or doctor blades.
One embodiment of the inventional apparatus consists in subdividing the applicators in a predosing apparatus for direct application of a surplus of liquid or pasty medium on one side of the traveling material web and a following separate final dosing apparatus serving to dose the amount of medium applied on the material web to the desired, final quantity. The predosing apparatus may be designed then as doctor/pressure chamber applicators, doctor/sump applicators, open-jet nozzle applicators or in comparable manner. The final dosing apparatus may be configured as doctor-blade final dosing apparatus or comparably.
Preferably, however, the applicators in the inventional apparatus are designed as finish-dosing applicators, that is, they allow applying a desired final amount of medium directly on the material web without requiring any finish dosing. The doctor/pressure chamber applicators or doctor/sump applicators explained above already are preferably used for that purpose.
A fourth inventional apparatus for application of a liquid or pasty medium on a traveling material web, notably of paper or cardboard, includes:
an open-jet nozzle applicator for direct application of a liquid or pasty medium on one side of a traveling material web,
a rotating press roll for pressing liquid or pasty medium applied on one side of the material web into the traveling material web, and
a press roll mating roll that rotates in a direction opposite to that of the press roll.
The open-jet applicator is coordinated with the top side of an unsupported section of the material web that extends substantially horizontally, while the press roll, based on the pass-through direction of the material web, is at a distance behind the open-jet applicator coordinated with the material web side coated with the medium previously and forms together with the mating roll a press nip through which the traveling material web is passed. The running direction of the press roll in the press nip corresponds to the pass-through direction of the material web.
Hence, a rotating mating face is dispensed with in the fourth inventional apparatus, that is, the applicator does not require a mating roll or a coordinated endless belt. The direct application of the liquid or pasty medium takes place along a substantially horizontally extending open draw of the material web. Viewed in the pass-through direction of the material web, before the position of the applicator, the arrangement of a reversing roll for instance is sufficient to deflect the material web in the substantially horizontal direction of travel.
The open-jet applicator in the fourth inventional apparatus is preferably configured as an applicator after the principle of a waterfall. In such applicator, the liquid or pasty medium to be applied flows in the fashion of a waterfall from the applicator, in an appropriately dosed amount, onto the material web that passes by beneath the applicator. The top side of the material web is in this way coated with the medium.
An advantage of the inventional apparatus is that providing press rolls separately allows adapting the material selection and surface properties of the press roll surface optimally to the requirements as regards a sound pressing process. In prior apparatus, where the liquid or pasty medium is applied first on the surface of an applicator roll and then transferred onto the traveling material web in a press nip (indirect application), the selection of applicator roll material and surface properties is governed primarily by the sound application of the medium on the roll surface, that is, by sound wetting of the surface. However, the material selection and the surface properties of the applicator roll cannot to an equal extent be adapted to the pressing function of the applicator roll in the applicator roll nip. With the application of the medium taking place inventionally now in a separate preceding step, directly onto the material web, and pressing the medium into the material web being carried out as a separate step of its own, the press rolls can with respect to their engineering and material-related configuration be adapted optimally to the pressing function.
In favorable embodiments, at least the surfaces of the press rolls are made of steel, rubber or polyurethane. In this context it may be favorable to provide the surfaces of the press rolls additionally with an antistick cover characterized by a comparatively low coefficient of friction. Such antistick cover consists preferably of a material on the basis of polytetrafluoroethylene (PTFE). Such Teflon coating counteracts sticking of the applied medium to the press rolls. Depending on their intended use, the press rolls may be provided with a maximally smooth, hard surface or with a soft surface having properties such that the applied medium will virtually not stick to it.
The peripheral speed of the press roll surface matches preferably the speed of travel of the material web in the press nip. Hence, there is no relative speed given between press roll surface and material web, so that the paper is practically not being stressed.
In one embodiment, the press rolls are equipped with a heating device that heats at least the roll surface, thereby accelerating the drying of the applied medium on the material web.
In another embodiment, a cleaning apparatus is coordinated with each press roll along a peripheral section of the roll surface. The cleaning apparatus features in a favorable embodiment a scraper blade which removes from the roll surface the dirt particles that separated from the material in the press nip. In conjunction with a coordinated cleaning apparatus it is favorable for the press roll surface to consist of a hard material, so that the surface quality of the press roll will not be impaired by the scraper blade or by accumulated dirt particles.
The inventional method and inventional apparatus serve especially the sizing of material webs, but just as well the application of most varied liquid or pasty coating mediums, sizing with pigments, starch, impregnating solution and the like. In the inventional method and inventional apparatus, the liquid or pasty medium is always applied directly on the material web, that is, without an intervening applicator roll, and the applied medium is always pressed into the material web separately from the process of applying the medium on the material web. Any contaminants or dirt particles which during pressing may separate from the traveling material web are in this way prevented from proceeding to the applicator and degrading the application quality of the medium on the traveling material web.